Implement granular cell updates on Python side

Author: krassowski

jupyter_ydoc/ynotebook.py

@@ -260,10 +260,28 @@ def set(self, value: dict) -> None:
                 cell_id = new_cell.get("id")
                 if cell_id and (old_ycell := old_ycells_by_id.get(cell_id)):
                     old_cell = self._cell_to_py(old_ycell)
-                    if old_cell == new_cell:
-                        new_cell_list.append(old_cell)
-                        retained_cells.add(cell_id)
-                        continue
+                    if old_cell != new_cell:
+                        # update cell granularly
+                        old_keys = set(old_cell.keys())
+                        new_keys = set(new_cell.keys())
+
+                        shared_keys = old_keys & new_keys
+                        removed_keys = old_keys - new_keys
+                        added_keys = new_keys - old_keys
+
+                        for key in shared_keys:
+                            if old_cell[key] != new_cell[key]:
+                                old_ycell[key] = new_cell[key]
+
+                        for key in removed_keys:
+                            del old_ycell[key]
+
+                        for key in added_keys:
+                            old_ycell[key] = new_cell[key]
+
+                    new_cell_list.append(old_cell)
+                    retained_cells.add(cell_id)
+                    continue
                 # New or changed cell
                 new_cell_list.append(new_cell)